Pd‐Catalyzed Cross‐Coupling of Alkylzirconocenes and Aryl Chlorides

Abstract

Comprehensive Summary Alkylzirconocenes, readily prepared by hydrozirconation of alkenes with Schwartz's reagent, are perspective yet rarely exploited partners in transition‐metal catalyzed cross‐coupling reaction. The notoriously low nucleophilicity of alkylzirconocenes and the potential β‐H elimination restrict their application in cross‐coupling. Herein, we report the first Pd‐catalyzed aryl‐alkyl cross‐coupling of alkylzirconocenes and aryl halides. A commercially available N‐heterocyclic carbene (IPr) as the ligand for palladium catalyst is critical to enable the challenging process. This mild protocol does not require base additives and tolerates a broad scope of both coupling partners bearing various functional groups and heterocycles. Moreover, both terminal and internal alkenes are applicable, and the latter undergo “chain walking”, giving the terminal coupling product exclusively. Preliminary mechanistic studies reveal a precatalyst activation pathway and inhibited β‐H elimination due to steric bulk of NHC ligand.

Nickel‐Catalyzed Transfer Hydrogenation of Unactivated Aryl Alkenes with Hydrosilane as Hydrogen Source

“…13 C NMR (101 MHz, CDCl 3 ) δ 142.5, 128.4, 128.2, 125.6, 35.8, 31.1. Spectroscopic data is consistent with the literature [34] …”

“…Spectroscopic data is consistent with the literature. [34] Gram Scale Synthesis of 3 a: To a flame dried 200 mL Schlenk flask was added Ni(acac) 2 (0.7 mmol, 179.9 mg), IMes • HCl (0.7 mmol, 238.7 mg), NaO t Bu (1.05 mmol, 100.8 mg) and E-1 a (7.0 mmol, 1.26 g), the flask was vacuumed and refilled with nitrogen three times. Then anhydrous toluene (70 mL), 2 a (28.0 mmol, 3.248 g) and H 2 O (7.0 mmol, 126 mg) was added with syringe under nitrogen atmosphere.…”

Recent advances in the application of ligands in palladium-catalyzed chemoselective coupling reactions at C–Br, C–OTf, and C–Cl sites

“…52 Jiang and Shi reported the first palladium-catalyzed crosscoupling reaction of aryl chlorides and alkyl zirconium reagents using C8 (Pd(i-Pr)(cin)Cl) to catalyze the C(sp 2 )-C(sp 3 ) coupling reaction. 140 One entry showed that the triflate group can be well tolerated in the system and preferentially reacted at the chloride with a 40% yield (Scheme 29).…”

Unsymmetric N-heterocyclic carbene ligand enabled nickel-catalysed arylation of bulky primary and secondary amines

“…We recently developed an array of bulky yet flexible NHCs 14 and applied them to a range of Ni-catalysed transformations, including challenging cross-coupling reactions. 15 We felt that a sterically demanding NHC ligand could promote R. E. At the same time, the conformational flexibility, available through rotatable single bonds on the ligand, may benefit coordination to the metal center, as well as oxidative addition (O. A.)…”